The present invention relates to a method of planarizing a substrate surface and a substrate with coating film. More particularly, the present invention relates to a method of planarizing an uneven surface of a substrate having an uneven surface, such as a semiconductor substrate, by forming a coating film thereon and relates to a substrate with coating film having its surface planarized by the above method, and a process for producing a semiconductor device, in which the above method is employed for planarizing an uneven surface of a semiconductor substrate.
With respect to various electronic components such as liquid crystal display elements for color display and semiconductor elements having a laminate structure, level differences attributed to, for example, wiring or a color filter occur on the substrate during a process of manufacture or production thereof and, therefore, it is needed to planarize the unevenness or irregularity caused by these level differences. In particular, with respect to semiconductor devices, it is needed to attain the complete planarization of the surface of an interlayer insulating film provided between wirings in order to realize a high-density integrated circuit.
Representative techniques for the above planarizing method are, for example, the hitherto proposed SOG (spin on glass) method, etch back method and lift-off method. For example, the SOG method comprises applying an SOG material consisting of a coating liquid containing an alkoxysilane such as Si(OR)4 on an uneven surface of a substrate and heating/curing the SOG material to thereby planarize the uneven surface of a substrate by forming an SOG film thereon, for which various processes have been proposed. Further, other than the above alkoxysilane, various organosilicon compounds have been proposed as a component of the SOG material.
However, the SOG method encounters the problem of the stability and superintendence of the coating liquid because the coating liquid is applied on the substrate. Moreover, the deterioration of hot carrier resistance of the MOS transistor attributed to the moisture contained in the SOG film has recently been reported and, hence, the control of moisture has also surfaced as a problem.
On the other hand, the etch back method encounters the problem of dust occurrence because the resist and insulating film are simultaneously etched. Thus, the etch back method is not an easy technique from the viewpoint of dust superintendence. Furthermore, the lift-off method encounters the problem of lift-off failure because employed stencil material is not completely dissolved away at the time of lift-off. Thus, the practical application of the lift-off method has not yet been realized because of the unsatisfactory controllability and yield.
The present invention has been made in these circumstances, and an object of the present invention is to provide a method of easily planarizing the uneven surface of a substrate having an uneven surface, a substrate with coating film which is excellent in flatness and has a uniform thickness, and a process for producing a semiconductor device with a planarized semiconductor substrate.
The method of planarizing a surface of a substrate having an uneven surface according to the present invention comprises the steps of:
forming a coating film containing spherical fine particles on a surface of a smooth substrate;
sticking the surface of the smooth substrate provided with the coating film containing spherical fine particles to the uneven surface of a substrate; and
transferring the coating film containing spherical fine particles to the uneven surface of the substrate so that the uneven surface is planarized.
In the present invention, the surface of the smooth substrate may be first furnished with a layer of spherical fine particles, and then a coating liquid may be applied onto the layer of spherical fine particles to thereby form the coating film containing spherical fine particles. Alternatively, the surface of the smooth substrate may be applied with a coating liquid for film formation which contains spherical fine particles on the uneven surface to thereby form the coating film containing spherical fine particles.
Further, the planarization of the uneven surface may be accomplished by the method wherein, at the time of transferring the coating film containing spherical fine particles to the uneven surface of the substrate, or thereafter,
the coating film containing spherical fine particles is heated so that at least part of the coating film is melted to thereby planarize the surface of the coating film, and
subsequently, the temperature is further raised so that the coating film containing spherical fine particles is cured to thereby accomplish the planarization of the uneven surface of the substrate.
It is preferred that the spherical fine particles are fine particles of silica, and that the coating film is a coating film containing a silicon-based component. Further, it is preferred that the coating film be formed from a coating liquid which contains a polysilazane having a repeating unit represented by the general formula [1]: 
wherein R1, R2 and R3 may be identical with each other or different from each other and represent a hydrogen atom, an alkoxy, aryl or alkyl having 1 to 8 carbon atoms, and n is an integer of 1 or greater.
The substrate with a coating film according to the present invention has its surface planarized by the above method.
The process for producing a semiconductor device according to the present invention comprises the steps of forming a coating film containing fine particles of silica by applying a coating liquid containing a polysilazane having a repeating unit represented by the above general formula [1] on a surface of a smooth substrate; and transferring the coating film containing fine particles of silica to an uneven surface of a semiconductor substrate so that the semiconductor substrate surface is furnished with the coating film containing fine particles of silica.